1. Field of the Invention
The present invention relates to supersonic air knife, more particularly a supersonic air knife handle and to a grasping handle assembly for a barrel, pipe or similar object.
2. Background Information
The present invention relates generally to air knives, and more specifically to the handles for supersonic air knives, and also to a grasping handle assembly for a barrel, pipe or similar object.
Air Knife Technology
In a conventional air knife associated with the present invention, compressed air, typically 90 to 100 psi, is converted to a supersonic jet while flowing through a nozzle especially designed for the purpose. The maximum jet velocity that can be achieved is determined by the pressure available from the compressor. Exit velocities in the range of Mach 1.6 to Mach 1.7 are typical for most portable compressors. Since the determining limit on Mach number for the exiting jet stream is the available pressure, higher Mach numbers can only be achieved by using higher compressor pressures. The air stream is initially the same diameter as the nozzle exit because the emerging jet stream diameter is the same as the nozzle exit diameter. For this reason, some refer to this characteristic as being laser-like. But as soon as the stream leaves the nozzle, it expands concentrically, since it is surrounded by atmospheric air.
High speed video of convention supersonic air knives shows the rapid expansion, but these videos also show that this high velocity air penetrates the ground to a depth of about a foot, creating a momentary cavity of about a foot in diameter, in which the dirt is crumbled. As the jet leaves that location or the air blast is ended, the dirt falls back on itself if the tool barrel is held close to the vertical. However, if the air knife barrel is inclined away from the user, the dirt can be blasted out the ground to a depth of one to two feet, depending upon technique. Since buried pipes, cables and tree roots are not porous the air knife use does not damage these elements, yet the dirt is removed from these structures. This aspect makes air knives quite popular for excavation of pipes and cables and for minimizing damage to ornamental trees.
For further details see regarding air knife technology and use see the inventors prior U.S. Pat. No. 8,171,659 entitled “Method and apparatus for selective soil fracturing, soil excavation or soil treatment using supersonic pneumatic nozzle with integral fluidized material injector;” and U.S. Pat. No. 8,171,659 entitled “Air Gun Safety Nozzle” which patents are incorporated herein by reference. U.S. Pat. Nos. 5,782,414, 5,212,891, 5,170,943, 4,813,611 all disclose related excavating pneumatic nozzle designs that are of interest and these are incorporated by reference as background. Representative examples of earlier air gun designs are shown in U.S. Pat. Nos. 3,599,876, 3,647,142, 3,672,575, 3,743,186, 3,774,847, 3,790,084, 3,790,085, 4,025,045, 4,026,474, 4,243,178, and 5,285,965 which are also incorporated herein by reference. From this prior art it can be seen that supersonic air knives are also referenced as compressed air guns, air blow guns, air jet guns, and a variety of similar terms. These will be referenced as supersonic air knives or air knives within this application.
The construction and operation of conventional air knives is known from the above cited prior art. There is a need for improved handles in the conventional supersonic air knives because of the elevated temperature of the compressed air passing through such a barrel. Some years ago in earlier air knife designs, this air was merely warm because portable air compressors had much larger stilling chambers in which the hot air from the compression process had time to mix and cool before entering the discharge air hose and then the supersonic air knife tool barrel. The original handle was wooden and glued to the barrel. The gluing was not reliable and the wood would dry and split in time as it was heated by the increasingly hot air generated by the compressed air flowing through the barrel interior.
This problem has continued over the years as compressor manufacturers gradually reduced the size of the stilling tank as a cost reduction measure until today they are so small the air heated by the compression process essentially receives no significant cooling affect from passing through current tanks as the further result of two routine requirements of today's typical supersonic air knife tool applications: large air mass flow and continuous or near continuous operation.
Thus plastic or rubber bicycle type handle grips replaced earlier wooden grips. These had the defect that an operator could easily allow their hand to slip up or down the barrel onto the hot portion of the barrel. Further these handle designs proved to be inadequate as a thermal insulator in practice due to the synergistic effect of the hot compressed air and the extreme environmental temperatures such as routinely occur in desserts or near dessert conditions.
More recently the air knife handles have been formed by commercially cast barrel claspers machining into two piece pipe hangers with threaded provision for a commercial handle or rod similarly threaded. The handle shifted the operator's grip away from the barrel to the handle for heat transfer isolation purposes. While this design was economical, it was prone to other problems. These barrel claspers have been of poor function, design and quality. They are also not convenient for the operator since the tightening screws require a separate tool (screw driver, Allen wrench, etc.) to reposition the handle assembly along the barrel. Pipe hangers usually require tightening in place on the pipe or barrel with a screw driver or wrench, and this construction is cumbersome when manual adjustments were desired to move the hanger along the barrel to a more useful position requiring loosening and then tightening the handle assembly in a new barrel position. Also, many hardware failures have been reported, in part because neither the pipe hanger hardware nor the plastic handle were intended for the more rigorous supersonic air knife applications as a construction tool. Such current hardware makes no provision for routine or random variation in barrel exterior shape or for unusual shapes. They provide no means of a controlled and predictable force multiplication which is necessary to avoid excessive hand torque sufficient to prevent slippage between handle assembly and barrel.
This invention is particularly useful for attachment to the barrel of supersonic air knives and addresses the problems of the prior art. The handle of the present invention may also serve as a grasping handle assembly for a barrel, pipe or similar object.